Interlaced Multiband Antenna Arrays

ABSTRACT

Antenna arrays which can work simultaneously in various frequency bands thanks to the physical disposition of the elements which constitute them, and also the multiband behavior of some elements situated strategically in the array. The configuration of the array is described based on the juxtaposition or interleaving of various conventional mono-band arrays working in the different bands of interest. In those positions in which elements of different multiband arrays come together, a multiband antenna is employed which covers the different working frequency bands. The advantages with respect to the classic configuration of using one array for each frequency band are: saving in cost of the global radiating system and its installation (one array replaces several), and its size and visual and environmental impact are reduced in the case of base stations and repeater stations for communication systems.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent application Ser. No. 14/529,715, filed on Oct. 31, 2014, which is a continuation of U.S. patent application No. 13/530,249, filed on Jun. 22, 2012, which is now U.S. Pat. No. 8,896,493, issued on Nov. 25, 2014, which is a continuation of U.S. patent application Ser. No. 13/044,831, filed on Mar. 10, 2011, which is now U.S. Pat. No. 8,228,256, issued on Jul. 24, 2012, which is a continuation of U.S. patent application Ser. No. 12/476,308, filed on Jun. 2, 2009, which is now U.S. Pat. No. 7,932,870, issued on Apr. 26, 2011, which is a continuation of U.S. patent application Ser. No. 11/803,782, filed on May 16, 2007, which is now U.S. Pat. No. 7,557,768, issued on Jul. 7, 2009, which is a continuation of U.S. patent application Ser. No. 10/988,261, filed on Nov. 12, 2004, which is now U.S. Pat. No. 7,250,918, issued on Jul. 31, 2007, which is a continuation of U.S. patent application Ser. No. 10/135,019, filed on Apr. 23, 2002, which is now U.S. Pat. No. 6,937,191, issued on Aug. 30, 2005, which is a continuation of International Application No. PCT/ES99/00343, filed on Oct. 26, 1999, the entire contents of which are hereby incorporated by reference.

BACKGROUND

The present invention consists of antenna arrays which can be operated simultaneously in various frequency bands thanks to the physical disposition of the elements that constitute it, as well as the multiband behavior of some elements situated strategically in the array.

The array configuration is described on a basis of the juxtaposition or interleaving of various conventional single-band arrays operating in the different bands of interest. In those positions where elements of different multiband arrays come together, use is made of a multiband antenna which covers the different working frequency bands.

The use of a multiband interleaved antenna array (hereinafter simply Multiband Interleaved Array, MIA) implies a great advantage over the classical solution of employing an array for each frequency band: there is a cost saving in the overall radiating system and in its installation (one array replaces several), its size is reduced as well as its visual and environmental impact in the case of base and repeater stations for communication systems.

The present invention finds its application in the field of telecommunications and more specifically in radio-communication systems.

Antennas started to be developed at the end of the nineteenth century based on the fundamental laws of electromagnetism postulated by James Clerk Maxwell in 1864. The invention of the first antenna has to be attributed to Heinrich Hertz in 1886 who demonstrated the transmission through air of electromagnetic waves. In the mid-1940's the fundamental restrictions regarding the reduction in size of antennas were shown with respect to wavelength and at the beginning of the sixties appeared the first frequency-independent antennas (E. C. Jordan, G. A. Deschamps, J. D. Dyson, P. E. Mayes, “Developments in Broadband Antennas,” IEEE Spectrum, vol. 1, pp. 58-71, April 1964; V. H. Rumsey, Frequency-Independent Antennas. New York Academic, 1966; R. L. Carrel, “Analysis and design of the log-periodic dipole array,” Tech. Rep. 52, Univ. of Illinois Antenna Lab., Contract AF33 (616)-6079, October 1961; P. E. Mayes, “Frequency Independent Antennas and Broad-Band Derivatives Thereof”, Proc. IEEE, vol. 80, no. 1, January 1992). At that time proposals were made for helical, spiral, log-periodic arrays, cones and structures defined exclusively by angle pieces for the implementation of broadband antennas.

Antenna array theory goes back to the works of Shelkunoff (S. A. Schellkunhoff, “A Mathematical Theory of Linear Arrays,” Bell System Technical Journal, 22,80), among other classic treatises on antenna theory. Said theory establishes the basic design rules for shaping the radiation properties of the array (principally its radiation pattern), though its application is restricted mainly to the case of mono-band arrays. The cause of said restriction lies in the frequency behavior of the array being highly dependent on the ratio between the distance between elements (antennas) of the array and the working wavelength. Said spacing between elements is usually constant and preferably less than one wavelength in order to prevent the appearance of diffraction lobes. This implies that once the spacing between elements is fixed, the operating frequency (and the corresponding wavelength) is also fixed, it being particularly difficult that the same array work simultaneously at another higher frequency, given that in that case the magnitude of the wavelength is less than the spacing between elements.

The log-periodic arrays suppose one of the first examples of antenna arrays capable of covering a broad range of frequencies (V. H. Rumsey, Frequency-Independent Antennas. New York Academic, 1966; R. L. Carrel, “Analysis and design of the log-periodic dipole array,” Tech. Rep. 52, Univ. Illinois Antenna Lab., Contract AF33 (616)-6079, October 1961; P. E. Mayes, “Frequency Independent Antennas and Broad-Band Derivatives Thereof”, Proc. IEEE, vol. 80, no. 1, January 1992). Said arrays are based on distributing the elements that constitute it in such a manner that the spacing between adjacent elements and their length vary according to a geometric progression. Although said antennas are capable of maintaining a same radiation and impedance pattern over a broad range of frequencies, their application in practice is restricted to some concrete cases due to their limitations regarding gain and size. Thus for example, said antennas are not employed in cellular telephony base stations because they do not have sufficient gain (their gain is around 10 dBi when the usual requirement is for about 17 dBi for such application), they usually have linear polarization whilst in said environment antennas are required with polarization diversity, their pattern in the horizontal plane does not have the width necessary and their mechanical structure is too bulky.

The technology of individual multiband antennas is markedly more developed. A multiband antenna is understood to be an antenna formed by a set of elements coupled to each other electromagnetically which interact with each other in order to establish the radio-electric behavior of the antenna, behavior which with respect to radiation and impedance patterns is similar in multiple frequency bands (hence the name multiband antenna). Numerous examples of multiband antennas are described in the literature. In 1995 antennas of the fractal or multifractal type were introduced (the coining of the terms fractal and multifractal is attributable to B. B. Mandelbrot in his book The Fractal Geometry of Nature, W. H. Freeman and Co. 1983), antennas which by their geometry have a multifrequency behavior and, in determined cases, a reduced size (C. Puente, R. Pous, J. Romeu, X. Garcia “Antenas Fractales o Mulitfractales,” (Spanish patent P9501019). Subsequently multi-triangular antennas were introduced (Spanish patent P9800954) which could work simultaneously in the GSM 900 and GSM 1800 bands and, more recently, multilevel antennas (Patent PCT/ES99/00296), which offer a clear example of how it is possible to shape the geometry of the antenna in order to achieve a multiband behavior.

SUMMARY

The present invention describes how multiband antennas can be combined in order to obtain an array that works simultaneously in several frequency bands.

A Multiband Interleaved Array (MIA) consists of an array of antennas which has the particularity of being capable of working simultaneously in various frequency bands. This is achieved by means of using multiband antennas in strategic positions of the array. The disposition of the elements that constitute the MIA is obtained from the juxtaposition of conventional mono-band arrays, employing as many mono-band arrays as frequency bands that it is wished to incorporate in the Multiband Interleaved Array. In those positions in which one or various elements originating in the conventional mono-band arrays coincide, a single multiband antenna (element) shall be employed which covers simultaneously the different bands. In the remaining non-concurrent positions, it can be chosen to employ also the same multiband antenna or else recur to a conventional mono-band antenna which works at the pertinent frequency. The excitation at one or various frequencies of each element of the array depends therefore on the position of the element in the array and is controlled by means of the signal distribution network.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics expounded in the foregoing, are presented in graphical form making use of the figures in the drawings attached, in which is shown by way of a purely illustrative and not restrictive example, a preferred form of embodiment. In said drawings:

FIG. 1 shows the position of the elements of two classic mono-band arrays which work at frequencies f and f/2 respectively, and the disposition of elements in a multiband interleaved array, which has a dual frequency behavior (at frequencies f and f/2), working in the same manner as classic arrays but with a smaller total number of elements.

FIG. 2 shows another particular example of multiband interleaved array but with three frequencies in this case, and the respective three classic mono-band arrays which constitute it. It is a matter of extending the case of FIGS. 1 to 3 frequencies f, f/2 and f/4.

FIG. 3 shows another particular example of multiband interleaved array, in which the different working frequencies are not separated by the same scale factor. It is a matter of extending the case of FIGS. 1 and 2 to 3 frequencies f, f/2 and f/3.

FIG. 4 shows a further particular example of multiband interleaved array, in which the different working frequencies are not separated by the same scale factor. It is a matter of extending the case of FIGS. 3 to 3 frequencies f, f/3 and f/4.

FIG. 5 shows a multiband interleaved array configuration which requires a repositioning of the elements to obtain frequencies that do not correspond to an integer factor of the highest frequency. In this particular example the frequencies f, f/2 and f/2.33 have been chosen.

FIG. 6 shows the extension of the design of an MIA to the two-dimensional or three-dimensional case, specifically, an extension of the example of FIG. 1 to two dimensions.

FIG. 7 shows one of the preferred of operating modes (AEM1). It is a matter of an MIA in which the multiband elements are multi-triangular elements. The array works simultaneously at dual frequencies, for example in the GSM 900 and GSM 1800 bands.

FIG. 8 shows another of the preferred operating modes (AEM2). It is a matter of an MIA in which the multiband elements are multilevel elements. The array works simultaneously at dual frequencies, for example in the GSM 900 and GSM 1800 bands.

FIG. 9 shows another of the preferred operating modes (AEM3). It is a matter of an MIA in which the multiband elements are multilevel elements. The configuration is similar to that of FIG. 8 (AEM2 mode), the difference being that the new disposition permits the total width of the antenna to be reduced.

FIG. 10 shows another example of multiband antenna which can be employed in MIAs. It is a matter of a stacked patch antenna, which in this specific example works at two dual frequencies (for example, GSM 900 and GSM 1800).

FIG. 11 shows the disposition of said patches in the MIA type array (AEM4 configuration). Observe that, in contrast to the previous cases, in this case multiband antennas are employed only in those positions where it is strictly necessary; in the remainder mono-band elements are employed the radiation pattern of which is sufficiently like that of the multiband element in the pertinent band.

FIG. 12 shows another configuration (AEM5), in which the elements have been rotated through 45° in order to facilitate the procurement of double polarization at +45° or −45°.

DETAILED DESCRIPTION

In making the detailed description that follows of the preferred embodiment of the present invention, reference shall constantly be made to the figures of the drawings, throughout which use has been made of the same numerical references for the same or similar parts.

A multiband interleaved array (MIA) is constituted by the juxtaposition of various conventional mono-band arrays. The conventional antenna arrays usually have a mono-band behavior (that is, they work within a relatively small frequency range, typically of the order of 10% about a center frequency) and this is not only because the elements (antennas) that constitute it have a mono-band behavior, but also because the physical spacing between elements conditions the working wavelength. Typically, the conventional mono-band arrays are designed with a spacing between elements of around a half-wavelength, spacing which may be increased in some configurations in order to enhance directivity, though it is usually kept below one wavelength to avoid the appearance of diffraction lobes.

This purely geometric restriction (the magnitude of the wavelength conditions the geometry of the elements of the array and their relative spacing) signifies a major drawback in those environments and communication systems in which various frequency bands have to be employed simultaneously. A clear example is the GSM cellular mobile telephony system. Initially located in the 900 MHz band, the GSM system has turned into one of the most widespread on a world scale. The success of the system and the spectacular growth in demand for this type of service has led to the cellular mobile telephony operators expanding its service into a new band, the 1800 MHz band, in order to provide coverage for a greater customer base. Making use of classic mono-band antenna technology, the operators have to duplicate their antenna network in order to provide coverage simultaneously to GSM 900 and GSM 1800. Using a single MIA specially designed for the system (like that described in the particular cases of FIGS. 7 through 12), the operators reduce the cost of their network of base stations, the time to expand into the new band and the visual and environmental impact of their installations (through the simplification of the overall radiating structure).

It is important to point out that the scenario which has just been outlined above deals only with one particular example of a type of MIA and its application; as may well be gauged by anyone familiar with the subject, in no way are the MIAs which are described in the present invention restricted to said specific configuration and can easily be adapted to other frequencies and applications.

The multiband interleaved arrays base their operation on the physical disposition of the antennas which constitute them and on the particular type of element that is employed in some strategic positions of the array.

The positions of the elements in an MIA are determined from the positions of the elements in as many mono-band arrays as there are frequencies or frequency bands required. The design of the array is, in that sense, equal to that of the mono-band arrays insomuch as it is possible to choose the current weighting for each element, in order to shape the radiation pattern according to the needs of each application. The configuration of the MIA is obtained from the juxtaposition of the positions of the different mono-band arrays. Naturally, such juxtaposition proves difficult to implement in practice in those positions in which various antennas of the different arrays coincide; the solution proposed in this invention rests in the use of a multiband antenna (for example of the fractal, multi-triangular, multi-level, etc. type) which covers all the frequencies associated with its position.

A basic and particular example of how to arrange the elements in an MIA is described in FIG. 1. In the columns of the FIG. 1 (1 a) and (1 b) two conventional mono-band arrays are shown in which the positions of the elements (indicated by the black circles and the circumferences respectively) are chosen in such a manner that the spacing between elements is typically less than the working wavelength. Thus, taking as reference the working frequency f of the array (1 a), the array (1 b) would work at a frequency f/2 as the elements have a spacing double that of the previous case. In FIG. 1 (column 1 c) the disposition is shown of the elements in the MIA which is capable of working simultaneously on the frequencies f and f/2 conserving basically the same facilities as the two arrays (1 a) and (1 b). In the positions in which elements of the two conventional arrays (indicated in FIG. 1 (1 c) by means of black circles located at the center of a circumference) coincide, a multiband antenna is employed capable of working in the same manner (same impedance and pattern) on the frequencies (1 a) and (1 b). The remaining not common elements (indicated either by a black circle, or by a circumference) can be implemented either by means of the same multiband element employed in the common positions (and selecting the working frequency by means of the signal distribution network of the array), or by employing conventional mono-band elements. In this example the array (1 c) has a dual behavior frequency-wise (at frequencies f and f/2), working in the same manner as the arrays (1 a) and (1 b) but with a smaller total number of elements (12 instead of 16).

Multiple examples of multiband antennas are already described in the state of the art. Antennas with fractal geometry, multi-triangular antennas, multi-level antennas even stacked patch antennas are some examples of antennas capable of working in like manner in multiple frequency bands. These, and other multiband elements can be employed in the positions of the MIAs in which elements of various mono-band arrays come together.

In the following figures other MIA configurations are shown, based on the same inventive concept, though having the disposition of the elements adapted to other frequencies. In FIG. 2 the configuration described is that of a tri-band MIA working at frequencies f, f/2 and f/4. The disposition of elements in the three classic mono-band arrays at the frequencies f, f/2 and f/4 is illustrated in the columns of FIGS. 2 (2 a), (2 b) and (2 c) by means of black circles, circumferences and squares respectively. The position of the elements of the MIA is determined from the configuration of the three mono-band arrays designed for each one of the three frequencies. The three arrays come together in the MIA that is shown in column 2 d of FIG. 2. In those positions where elements of the three arrays would come together (indicated in the drawing by the juxtaposition of the different geometric figures identifying each array) use is made of a multiband element. The three-frequency array of column (2 d) behaves in the same manner as the three arrays (2 a), (2 b) and (2 c) at their respective working frequencies, but employing only 13 elements instead of the 21 required in the total of the three mono-band arrays.

FIGS. 3, 4 and 5 describe, by way of example and not restrictively, the design of other MIAs based on the same principle though at other frequencies. In the first two cases the frequencies employed are integer multiples of a fundamental frequency; in the case of FIG. 5 the ratio between frequencies is not restricted to any particular rule, though it supposes an example of array in which the frequencies the GSM 900, GSM 1800 and UMTS services can be combined.

Specifically, FIG. 3 illustrates another particular example of multiband interleaved array, in which the different working frequencies are not separated by the same scale factor. It concerns the extension of the case of FIGS. 1 and 2 to 3 frequencies f, f/2 and f/3. The disposition of elements of the three classic mono-band arrays at the frequencies f, f/2 and f/3 is shown in the columns of FIGS. 3 (3 a), (3 b) and (3 c) by means of black circles, circumferences and squares respectively. The column (3 d) of FIG. 3 shows the disposition of elements in the tri-band interleaved array. In those positions in which elements of the three arrays come together (indicated in the drawing by the juxtaposition of the different geometric figures identifying each array), use is made of a multiband element; the same strategy is followed in those positions in which elements of two arrays coincide: use should be made of a multiband element capable of covering the frequencies pertinent to its position, preferentially the same element as that used in the remaining positions, selecting those frequencies which are necessary by means of the feeder network. Notice that as the three-frequency array of column (3 d) of FIG. 3 behaves in the same manner as the three arrays (3 a), (3 b) and (3 c) at their respective working frequencies, but employing only 12 elements instead of the 21 required in the total of the three mono-band arrays.

FIG. 4 illustrates a new particular example of multiband interleaved array, in which the different working frequencies are not separated by the same scale factor. It concerns the extension of the case of FIGS. 3 to 3 frequencies f, f/3 and f/4. The disposition of elements of the three classic mono-band arrays at the frequencies f, f/3 and f/4 are shown in the columns of FIGS. 4 (4 a), (4 b) and (4 c) by means of black circles, circumferences and squares respectively. The column (4 d) of FIG. 4 shows the disposition of elements in the tri-band interleaved array. In those positions where elements of the three arrays would come together (indicated in the drawing by the juxtaposition of the different geometric figures identifying each array), use is made of a multiband element. The three-frequency array of column (4 d) of FIG. 4 behaves in the same manner as the three arrays (4 a), (4 b) and (4 c) at their respective working frequencies, but employing only 15 elements instead of the 24 required in the total of the three mono-band arrays.

It is convenient to re-emphasis that in the particular cases of FIGS. 3 and 4 the arrays can work at 3 frequencies simultaneously. The disposition of elements is such that the three frequencies do not always coincide in all the elements; nonetheless, by employing a tri-band antenna in those positions and selecting the working frequencies for example by means of a conventional frequency-selective network, it is possible to implement the MIA.

In some configurations of multiband interleaved array, especially in those in which the different frequencies do not correspond to an integral factor of the highest frequency 1, it is required that the elements be repositioned, as in FIG. 5. In this particular example the frequencies f, f/2 and f/2,33 have been chosen. The disposition of elements of the three classic mono-band arrays at the frequencies f, f/2 and f/2.33 is represented in the columns of FIGS. 5 (5 a), (5 b) and (5 c) by means of black circles, circumferences and squares respectively. The column (5 d) of FIG. 5 shows what would be the disposition of elements in the tri-band interleaved array according to the same plan as in the previous examples. Notice how in this case the ratio of frequencies involves the collation of elements at intermediate positions which make its practical implementation difficult. The solution to be adopted in this case consists in displacing the position of the element of the array that works at the lowest frequency (indicated by arrows) until it coincides with another element (that nearest) of the highest frequency array; then the two or more coincident elements in the new position are replaced with a multiband element. An example of the final configuration once the elements have been repositioned, is shown in column (5 e) of FIG. 5. It is important that the element displaced be preferentially that of the lowest frequency array, in this way the relative displacement in terms of the working wavelength is the least possible and the appearance of secondary or diffraction lobes is reduced to the minimum.

FIG. 6 illustrates how the configuration MIAs is not limited to the linear (one-dimensional) case, but it also includes arrays in 2 and 3 dimensions (2D and 3D). The procedure for distributing the elements of the array in the 2D and 3D cases is the same, replacing also the different coincident elements with a single multiband antenna.

More examples of particular configurations of MIAs are described below. In the five examples described, various designs are presented for GSM 900 and GSM 1800 systems (890 MHz-960 MHz and 1710 MHz-1880 MHz bands). It is a question of antennas for cellular telephony base stations, which present basically the same radiofrequency behavior in both bands; by employing such versions of MIA antenna the operators reduce the number of antennas installed to one half, minimizing the cost and environmental impact of their base stations.

AEM1 Mode

The AEM1 configuration, represented in FIG. 7, is based on the use of GSM 900 and GSM 1800 multi-triangular elements. The array is obtained by interleaving two conventional mono-band arrays with spacing between elements less than one wavelength in the pertinent band (typically a spacing is chosen less than 0.9 in order to minimize the appearance of the diffraction lobe in the end-fire direction). The original arrays can have 8 or 10 elements, depending on the gain required by the operator. The juxtaposition of both arrays in a single MIA is achieved in this case by employing dual multi-triangular elements. Such elements incorporate two excitation points (one for each band), which allows the working band to be selected according to their position in the array. In FIG. 7 the position of the elements is shown, as well as their working frequencies. The elements shown in white indicate operation in the GSM 900 band; the elements shown in black indicate operation in the GSM 1800 band and the elements marked in black in the lower triangle and in white in their two upper triangles indicate simultaneous operation in both bands. Precisely the simultaneous operation in both bands via a single multiband element (the multi-triangular element) in such positions of the array (those positions at which those of the original mono-band arrays coincide), is one of the main characteristic features of the MIA invention.

The manner of feeding the elements of the AEM1 array is not characteristic of the invention of the MIAs and recourse may be had to any conventionally known system. In particular and given that the multi-triangular elements are excited at two different points, it is possible to make use of an independent distribution network for each band. Another alternative consists in employing a broadband or dual band distribution network, by coupling a combiner/diplexer which interconnects the network and the two excitation points of the multi-triangular antenna.

Finally, the antenna may therefore come with two input/output connectors (one for each band), or combined in a single connector by means of a combiner/diplexer network.

AEM2 Mode

This particular configuration of AEM2, shown in FIG. 8, is based on a multilevel antenna which acts as a multiband element. In addition to working simultaneously in the GSM 900 and GSM 1800 bands, the antenna has also double linear polarization at +45° and −45° with respect to the longitudinal axis of the array. The fact that the antenna has double polarization signifies an additional advantage for the cellular telephony operator, since in this manner he can implement a diversity system which minimizes the effect of fading by multipath propagation. The multilevel element which is described in FIG. 8 is more suitable than the multi-triangular element described previously since the element itself has a linear polarization at +45° in GSM 900 and at −45° in GSM 1800.

The array is obtained by interleaving two conventional mono-band arrays with spacing between elements less than one wavelength in the pertinent band (typically a spacing less than 0.9 is chosen in order to minimize the appearance of the diffraction lobe in the end-fire direction). The original arrays can have 8 or 10 elements depending on the gain required by the operator. The juxtaposition of both arrays in a single MIA is achieved in this case by employing in-band dual multilevel elements. Such elements incorporate two points of excitation (one for each band), which permits the working band to be selected according to their position in the array. In FIG. 8 the position of the elements is shown, as well as their working frequencies. The elements shown in white indicate operation in the GSM 900 band; the elements shown in black indicate operation in the GSM 1800 band and the elements marked in black in their lower triangle and in white in the upper triangles indicate simultaneous operation in both bands. Precisely the simultaneous operation in both bands via a single multiband element (the multilevel element) in such positions of the array (those positions in which those of the original mono-band arrays coincide), is one of the main characteristic features of the MIA invention.

It is possible to achieve double polarization on a basis of exciting the multilevel element at various points on its surface, nonetheless in order to augment the isolation between connectors of different polarization, it is chosen in the example described to implement a double column to separate the +45° polarization (left-hand column) from that of −45° (right-hand column). To increase the isolation between bands, it is even possible to interchange the polarization inclination in the columns of the array in one of the bands (for example in DCS).

The manner of feeding the elements of the array AEM2 is not characteristic of the invention of the MIAs and recourse can be had to any conventionally known system. In particular and given that the multi-triangular elements are excited at two different points, it is possible to make use of an independent distribution network for each band and polarization. Another alternative consists in employing a broadband or dual band distribution network, by coupling a combiner/diplexer which interconnects the network and the two excitation points of the multilevel antenna. The antenna may then come with four input/output connectors (one for each band and polarization), or else combined in only two connectors (one for each independent polarization) by means of combiner/diplexer network in each polarization.

AEM3 Mode

The AEM3 configuration, as shown in FIG. 9, is very similar to the AEM2 (the position of the multilevel elements and the type of element itself is the same as in the previous case), with the difference that the right-hand column is reversed with respect to that on the left. In this manner an antenna with dual band and polarization is obtained, the total width of the antenna being reduced with respect to the previous case (in this particular example the width is reduced by about 10%). In order to increase the isolation between the columns of double polarization it is convenient that oblique fins be inserted between contiguous elements. In that case, lateral fins are also incorporated in all the elements which work in GSM 1800, fins which contribute to narrowing the radiation beam in the horizontal plane (plane at right angles to the longitudinal axis of the array).

Nor is the signal distribution system especially characteristic of the MIA configuration and the same system can be used as in the previous case.

AEM4 Mode

Another example of multiband interleaved array is that termed herein AEM4 and which is shown in schematic form in FIG. 11. In this case, the multiband element is a stacked square patch antenna (FIG. 10), though it is obvious for anyone familiar with the subject that patches of other shapes could be employed. Square- or circular-shaped types are preferred in the event that is wished to work with double polarization. In the example of FIG. 10 the particular case is described of square patches.

The lower patch is of appropriate size for its resonant frequency (associated typically with the patch fundamental mode) to coincide with the lower band (GSM 900 in this specific case); moreover, this patch acts in turn as ground plane of the upper patch. The latter is of a size such that its resonance is centered in the upper band (GSM 1800). The elements of the array are mounted on a metallic or metal-coated surface which acts as ground plane for all the elements of the array. The feeder system is preferentially of the coaxial type, a cable being employed for the lower patch and band and another for the upper patch and band. The excitation points are collated on the bisectors of the patches (for example, the approximate excitation points are marked by means of circles on the plan view of the antenna) if vertical or horizontal polarization is desired, or on the diagonals if, on the other hand, linear polarization inclined at 45° is desired. In the event it is desired that the array work with double polarization, each of the patches is excited additionally on the bisector or diagonal opposite (orthogonal) to the first.

The feeding of the elements of the array AEM4 is not characteristic of the invention of the MIAs and recourse can be had to any conventionally known system. In particular and given that the stacked patch antenna is excited at two different points, it is possible to make use of an independent distribution network for each band and polarization. Another alternative consists in employing a broadband or dual band distribution network, by coupling a combiner/diplexer which interconnects the network and the two excitation points of the multilevel antenna.

The antenna may then come with four input/output connectors (one for each band and polarization), or else combined in only two connectors (one for each independent polarization) by means of a combiner/diplexer network in each polarization.

AEM5 Mode

The AEM5 configuration, as shown in FIG. 12, adopts the same approach as the AEM4, though all the elements are rotated through 45° in the plane of the antenna. In this manner the radiation pattern is modified in the horizontal plane, in addition to rotating the polarization through 45°.

It is of interest to point out that both in the AEM4 configuration and in the AEM5, the multiband element constituted by the stacked patches is really only strictly necessary in those strategic positions in which elements originating in the conventional mono-band arrays coincide. In the remaining positions, it shall be possible to employ indistinctly multiband or mono-band elements that work at the frequency determined for its location, as long as its radiation pattern is sufficiently like that of the stacked patch antenna in order to avoid the appearance of diffraction lobes.

It is not deemed necessary to extend further the content of this description in order that an expert in the subject can comprehend its scope and the benefits arising from the invention, as well as develop and implement in practice the object thereof.

Notwithstanding, it must be understood that the invention has been described according to a preferred embodiment thereof, for which reason it may be susceptible to modifications without this implying any alteration to its basis, it being possible that such modifications affect, in particular, the form, the size and/or the materials of manufacture. 

What is claimed is:
 1. An antenna array comprising: a ground plane layer; a first set of antenna elements arranged on the ground plane layer and being configured to provide operation of the antenna array in at least three frequency bands respectively corresponding to three cellular frequency bands; a second set of antenna elements arranged on the ground layer and being configured to provide operation of the antenna array in two of the three frequency bands; the first set of antenna elements and the second set of antenna elements are substantially arranged along a longitudinal direction of the antenna array; the first set of antenna elements and the second set of antenna elements are arranged on alternating positions along the longitudinal direction; and wherein a ratio of a spacing between antenna elements of the first set to a wavelength of a first frequency band of the three frequency bands is substantially half of a ratio of a spacing between antenna elements of the second set to a wavelength of a second frequency band of the three frequency bands.
 2. The antenna array of claim 1, wherein a ratio between a frequency of the third frequency band and a frequency of the second frequency band is less than 1.5.
 3. The antenna array of claim 1, wherein a frequency for the first frequency band is situated around 900 MHz, a frequency for the second frequency band is situated around 1800 MHz, and a frequency for the third frequency band is situated around 2100 MHz.
 4. The antenna array of claim 1, wherein the three frequency bands are not separated by the same scale factor.
 5. A communication system comprising: a network of base stations comprising a plurality of base stations, at least some of the plurality of base stations comprising the antenna array of claim
 1. 6. An antenna array comprising: a ground plane layer; a first plurality of antenna elements arranged on the ground plane and being configured to provide operation of the antenna array in at least first and second frequency bands respectively corresponding to two cellular frequency bands, the first and second frequency bands being non-overlapping frequency bands; and a second plurality of antenna elements arranged on the ground plane layer and being configured to provide operation of the antenna array in the second frequency band, wherein the first plurality of antenna elements and the second plurality of antenna elements are substantially arranged along a longitudinal direction of the antenna array; and a ratio of a spacing between antenna elements providing operation at the first frequency band to an operating wavelength of the first frequency band is substantially the same as a ratio of a spacing between antenna elements providing operation at the second frequency band to an operating wavelength of the second frequency band.
 7. The antenna array of claim 6, wherein the antenna elements of the first plurality and the antenna elements of the second plurality are arranged in alternating positions along the longitudinal direction of the antenna array.
 8. The antenna array of claim 7, wherein a ratio between an operating frequency of the second frequency band and an operating frequency of the first frequency band is greater than two.
 9. The antenna array of claim 6, wherein each antenna element of the first plurality of antenna elements comprises a plurality of electromagnetically coupled portions configured to interact with each other.
 10. The antenna array of claim 9, further comprising a first distribution network configured to excite the first plurality of antenna elements, and a second distribution configured to excite the antenna elements providing operation at the second frequency band.
 11. A communication system comprising: a network of base stations comprising a plurality of base stations, at least some of the plurality of base stations comprising the antenna array of claim
 6. 12. An antenna array comprising: a ground plane layer; a plurality of antenna elements arranged on the ground plane layer along a longitudinal direction of the antenna array; a first distribution network configured to excite the plurality of antenna elements for a first polarization; and a second distribution network configured to excite the plurality of antenna elements for a second polarization, the first and second polarizations being orthogonal polarizations, wherein: the plurality of antenna elements are configured to provide operation of the antenna array in three frequency bands respectively associated with three cellular frequency bands; the highest frequency of a first frequency band of the three frequency bands is less than the lowest frequency of a second frequency band of the three frequency bands and the lowest frequency of a third frequency band of the three frequency bands is greater than the highest frequency of the second frequency band; a ratio between a frequency of the third frequency band and a frequency of the first frequency band being smaller than 1.5; a spacing between the antenna elements of the plurality of antenna elements is less than a wavelength of the lowest operating frequency of the first frequency band; and a spacing between the antenna elements of the plurality of antenna elements is greater than a half wavelength of the highest frequency of the third frequency band.
 13. The antenna array of claim 12, wherein a first spacing between a first pair of adjacent antenna elements of the plurality of antenna elements is different from a second spacing between a second pair of adjacent antenna elements of the plurality of antenna elements.
 14. The antenna array of claim 12, wherein any operating frequencies of the third frequency band does not correspond to an integer factor of an operating frequency of the first frequency band.
 15. The antenna array of claim 12, wherein the three frequency bands are not separated by the same scale factor.
 16. The antenna array of claim 12, wherein the antenna elements of the plurality of antenna elements comprises patch antennas.
 17. A communication system comprising: a network of base stations comprising a plurality of base stations, at least some of the plurality of base stations comprising the antenna array according to claim
 12. 